Steve Jobs, who died today, resigned as chief executive of Apple in August.

The 55-year-old Apple co-founder and pancreatic cancer survivor had been on medical leave for an undisclosed condition since January 17.

Here is a chronology of his health issues:

2004:

August: Jobs announces he underwent surgery to remove a cancerous tumour from his pancreas. He said it was a rare form of pancreatic cancer called an islet cell neuroendocrine tumour, which often is not quite as deadly as the more common forms of pancreatic cancer. The tumours can cause hormone imbalances.

2005:

June : Jobs mentions the cancer in a commencement address at Stanford University.

"This was the closest I have been to facing death, and I hope it is the closest I get for a few more decades," he says.

2008:

June 9: Jobs appears dramatically thinner at an Apple iPhone event, touching off speculation the cancer had returned. The company said he was fighting a "common bug" and taking antibiotics. Apple later called Jobs's health a private matter.

July 26: The New York Times journalist Joe Nocera said in a column he had spoken to Jobs about his health but because the conversation was off record, he could not disclose what was said.

"While his health problems amounted to a good deal more than 'a common bug', they were not life-threatening and he does not have a recurrence of cancer," Nocera wrote.

September 9: At an iPod product launch, Jobs jokes about his health by walking on stage in front of a giant screen that flashed "The reports of my death are greatly exaggerated" - a quotation borrowed from Mark Twain.

October 3: A false internet report that Jobs had suffered a heart attack briefly pushes Apple shares down 2 percent to a 17-month low. Apple quickly denied the report on iReport.com, a citizen journalist site owned by CNN.

October 14: At a Mac product launch event, Jobs jokes again about his health. His blood pressure was 110 over 70 and he said, "And that is all we are going to be talking about Steve's health today."

December 16: Apple said Jobs would not deliver the keynote address at the Macworld trade show in January, reviving concerns about his health.

Asked to explain the decision, a spokesman said it would be the last time Apple takes part in Macworld so, "it does not make sense for us to make a major investment in a trade show we will no longer be attending."

December 30: Apple shares fall as much as 2 percent after Gizmodo said that Jobs's health was "rapidly declining" and that was the reason why he cancelled the Macworld keynote.

2009:

January 5: Jobs says he has been losing weight throughout 2008 and his doctors think a hormone imbalance is "robbing" him of proteins. He says he has begun a "relatively simple and straightforward" treatment for his nutritional problem and that he will continue as CEO during recovery.

January 21: The US Securities and Exchange Commission is examining Apple's disclosures about Jobs to ensure investors were not mislead, Bloomberg says.

June 8: Apple unveils new iPhone 3GS at its annual Worldwide Developer's Conference, but Jobs does not make an appearance.

June 20: The Wall Street Journal reports that Jobs had a liver transplant in Memphis, Tennessee about two months before and that he is expected to return to work later in June.

June 22: Jobs is spotted at the Apple campus in Cupertino, California, underscoring expectations that he is either back at work or will return soon.

June 23: The Methodist University Hospital Transplant Institute confirms it performed a liver transplant on Jobs and says he is "recovering well and has an excellent prognosis." The hospital does not give more details, saying the confirmation had come with Jobs's permission.

Organ transplant recipients often have recurring health issues for life, in part because they must take immune-suppressing drugs to prevent organ rejection or graft versus host disease.

June 30: Jobs returns to work, an Apple spokesman says. adding that he will work from home part of the time.

2011:

January 17: Jobs says he will take medical leave from Apple. Cook will take responsibility for day-to-day operations but Jobs will continue to be chief executive and be involved in major strategic decisions.

"I love Apple so much and hope to be back as soon as I can," the 55-year-old says. Apple shares were down 8.3 percent in Frankfurt by 1503 GMT. Monday was a holiday in the United States and markets were closed there.

March 2: A thin but energetic Jobs makes a surprise return to the spotlight, taking the stage to unveil Apple's new iPad and drawing a standing ovation.

June 6: Animated but again looking very thin, Jobs appears at Apple's Worldwide Developers' Conference and unveils services for people to store more of their photos, music and other data online, giving the iPad and iPhone maker the lead in a fast-expanding new consumer market.